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Reseeding Crimson Clover as a N Source for No-Tillage Grain Sorghum Production¹

Nitrogen fertilizer is an expensive but essential input for optimum production of non-leguminous crops. The use of N fertilizer for summer grain crops can be reduced and possibly eliminated by double cropping with leguminous winter crops. Costs of seeding winter legumes, however, are often as expensive as the commercially produced N that they replace. Allowing the legumes to produce seed prior to planting the summer crop may potentially eliminate costs associated with seeding the legume each fall. The purpose of this field study, conducted on a Cecil sandy loam soil (Typic Hapludult), was to determine N fertilizer requirements for no-tillage grain sorghum (Sorghum bicolor L. Moench) double cropped with reseeding crimson clover (Trifolium incarnation L.) and effects of N treatments on nutrient uptake and on insect populations. Nitrogen treatments were 0, 15, 30, 45, 90, and 135 kg N/ha and the clover tissue was either removed or left on the soil surface as a no-tillage mulch.

No-till planting sorghum into clover or removing the clover top growth at maturity had no apparent effect on clover stand establishment the following fall. Clover dry matter production was essentially equal among years and averaged 4,762 kg/ha/yr. When averaged over years, the N, P, and K concentrations in the clovertops were 2.02, 0.24 and 2.40%, respectively. The only essential nutrient in sorghum leaves at the bloom stage affected by applied N was Cu which increased linearly as applied N increased. The only effects that removing clover had on nutrient content in the sorghum leaves were to reduce K in 1979 (from 2.47 to 2.31%), N in 1980 (from 2.85 to 2.69%) and P in 1979 (from 0.36 to 0.34%) and 1980 (from 0.34 to 0.29%). The reductions, however, were not sufficient to create a deficiency of either element. Some differences were found among common insect populations and their subsequent damage among treatments but the populations were not great enough to be considered economically damaging. Nitrogen produced by the clover was sufficient for maximum sorghum grain yield (5,760, 7,098, and 2,924 kg/ha in 1978, 1979, 1980, respectively) without supplemental applications of inorganic N. Removing the clover had no effect on sorghum grain yield in 1978 or 1979, but in 1980 this treatment reduced grain yield 601 kg/ha. Even though removing the clover which contained 62 kg/ha N in 1980 reduced sorghum yield, there was no response to applied N which suggests that the yield reduction was not due to a shortage of N.

Key Words: Conservation tillage • Insect population and damage • Leaf nutrient content • Double cropping • Sorghum bicolor L. Moench • Trifolium incarnatum L.

² Assistant professors, soil fertility, entomology, soil fertility, and sorghum breeding/physiology, respectively. Senior author is now associate professor, Dep. of Agronomy and Soils, Auburn Univ., Auburn, AL 36849.

Received for publication July 2, 1981.

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